The international patent application WO 2011/159171 describes a passive RFID device with an UHF interface comprising an UHF antenna and a dual frequency LF-HF Interface comprising a LF antenna and a HF antenna. The dual frequency LF-HF Interface carries out a IP-X protocol in which only a LF demodulator and a HF modulator is used. It is to be noted that the dual frequency LF-HF interlace is intended to communicate with a single dual frequency reader. The passive RFID device further comprises a UHF rectifier and a LF rectifier which can both generate a power supply for this device. More particularly, a decision circuit is provided for selecting either the LF rectifier or the UHF rectifier as power generator depending on which one delivers the largest signal.
The passive RFID device further comprises a controller formed by a UHF logic unit, a IP-X logic unit and a single shared non-volatile memory (EEPROM). The device is arranged for detecting which kind of readers is present and for responding accordingly. More particularly, depending on which energy source is present and the strength of that energy source, the controller select either the UHF logic unit or the IP-X logic unit or both and executes respectively a UHF protocol, a IP-X protocol or both. According to the document WO 2011/159171, it is an important aspect that the same data be delivered to both UHF and dual frequency readers. For this purpose, a single EEPROM memory is used by each protocol and fully shared between the UHF logic unit and the IP-X logic unit. In order to allow such a full sharing of the single EEPROM memory, a different mapping is provided for both protocols.
This prior art RFID device has some drawback, a major one being the fact that the sensitivity of the UHF interface is relatively low due to the fact that there is a single non-volatile memory (also named NVM in the following text) which is accessed by both interfaces. Indeed, the whole EEPROM memory is powered when one or the other interface carries out its corresponding protocol. This is a problem because the IP-X protocol or more generally a LF or HF protocol needs a relatively big non-volatile memory which consumes a relative high power. The activation of such a big NVM and the access to this memory is power hungry, so that the power level needed for carrying out the UHF protocol is much higher than in a UHF system formed by a UHF transponder and a UHF reader. As a consequence, the distance of communication for a UHF communication in the system proposed by WO 2011/159171 is shorter than the corresponding distance of the mentioned UHF system.